In recent years, a variety of moving vehicles have been developed, including hybrid motor vehicles, electrically-assisted bicycles, and industrial conveying vehicles used for conveyance within a factory. Such moving vehicles have a motor as a power source, therefore a battery pack for supplying electricity to the motor is a significant component. Such being the case, the battery pack has been improved in various ways. For example, in the technology described in Patent Document 1, a temperature sensor and heater are attached to a battery pack, and decline in function of the battery pack caused by low temperature is prevented by increasing the temperature using the heater.
In a general structure of a battery pack, a plurality of battery cells are connected in series to construct an assembled battery, and the assembled battery is disposed in a pack case. As the battery cells, it is appropriate to use a lithium-ion battery that can be subjected to replenishment charging when the battery wears out. Such a battery pack is installed with a power supply connector that has an insertion part to which a charging plug is inserted, and this power supply connector charges the battery from an external power supply.
In a normal power supply connector, the insertion part is provided in a connector front surface part that is exposed to a pack case outer surface part of a battery pack, and the charging plug connected to the external power supply is inserted into this insertion part. Moreover, two connector pins that extend backward from the insertion part are disposed on the rear surface part side of the power supply connector.
A circuit board provided with a protection circuit or a metal plate such as a bus bar is connected to the connector pins and charging is performed by feeding a current from the external power supply to the assembled battery within the pack case.
It is required for such a battery pack to carry out large current charging (at least 30 A) suitable outside of home or within a factory, not to mention low current charging (less than 30 A) using a household power supply. For this reason, in the power supply connector installed in the battery pack, two types of charging plugs, a large current charging plug and a low current charging plug, are inserted desirably so that large current charging and low current charging can be executed.
On the other hand, in order to obtain a power supply connector applicable to both large current charging and low current charging, there has been developed a power supply connector provided with two types of insertion parts on the front surface part side, to which the two types of plugs are inserted, and two types of connector pins on the rear surface part side, which extend backward from the insertion parts. Here, the large current charging plug is relatively larger than the low current charging plug. Thus, in order to conform with the size of the plugs, a large current charging insertion part or connector pin of the power supply connector are larger than a low current charging insertion part or connector pin.
Therefore, the conventional power supply connector applicable to large current charging has the following problems due to the large-diameter large current charging connector pin. The configuration of the conventional power supply connector is now illustrated in detail with reference to the side view of FIG. 7, and the problems of the large-diameter large current charging connector pin are described.
As shown in FIG. 7, the power supply connector 1 is disposed in a pack case of a battery pack capable of being subjected to replenishment charging, wherein the large-diameter large current charging connector pin 2 is disposed on the rear surface side (on the right rim part side in FIG. 7). The large current charging connector pin 2 extends backward from a rear surface part of the power supply connector 1 (to the right in FIG. 7), and a circuit board or metal plate 3 that is embedded in the battery pack is installed below the large current charging connector pin 2.
The large current charging connector pin 2 is connected to the circuit board or the metal plate 3. Because the large current charging connector pin 2 has a large diameter and thus requires a space in a height direction, which reduces the volumetric efficiency of the power supply connector 1. Moreover, because of the large diameter of the large current charging connector pin 2, the cross-sectional area of the connecting wiring that connects the large current charging connector pin 2 with the circuit board or the metal plate 3 increases. Therefore, the amount of heat generated in the section of this connecting wiring is large.
In addition, the large cross-sectional area of the connecting wiring connecting the large current charging connector pin 2 with the circuit board or the metal plate 3 makes the connecting work itself difficult and consequently reduces the workability. Especially a battery pack of an electric bicycle needs to be made strong against shock such as vibration and sideway push, thus it is essential to ensure excellent connection strength and a reliable connecting work. Therefore, it is urgent to improve the work efficiency in the work of connecting the large current charging connector pin 2 with the circuit board or the metal plate 3.
On the other hand, as one of the methods for obtaining the power supply connector applicable to both large current charging and low current charging, there is considered a method for using the same connector pin in both large current charging and low current charging to enhance space utilization and improve the volumetric efficiency of the power supply connector. However, when using the same connector pin in both large current charging and low current charging, the size of the connector pin always needs to match the size corresponding to large current charging.
For this reason, in the circuit board connected to the connector pin, it is inevitable to adopt a circuit suitable for monitoring large current charging, as a protection circuit used for monitoring charging. As a result, not only the accuracy of monitoring low current charging but also the volumetric efficiency of the circuit board is reduced, causing a cost increase.
In order to maintain the accuracy of monitoring low current charging and the volumetric efficiency of the circuit board, there is considered a method for providing separately a large current charging connector pin with a large diameter and a low current charging connector pin with a small diameter, and providing separately a special protection circuit suitable for monitoring low current charging and a special protection circuit suitable for monitoring large current charging. In this case, the large current charging connector pin has a large diameter and the low current charging connector pin has a small diameter. Regarding the insertion parts for inserting charging plugs thereto, because a low current charging insertion part is smaller than a large current charging insertion part, a large current charging connector part having the insertion part and the connector pin is larger than a low current charging connector having the same.
Here, FIGS. 8 and 9 are used for described an example of a conventional connector that has two types of connector parts, a large current charging connector and a low current charging connector. In a power supply connector 1 shown in FIG. 8, two large current charging current pin insertion parts 14 included in a large current charging connector part, and two low current charging current pin insertion parts 15 included in a low current charging connector part are arranged in a line from the left to the right of the diagram. In a power supply connector 1 shown in FIG. 9, two large current charging current pin insertion part 14 are arranged on the lower side, and two low current charging current pin insertion parts 15 are arranged thereabove, forming a two-stage configuration.    {Patent Document 1}: 2004-362949
However, the conventional power supply connectors 1 shown in FIGS. 8 and 9 have the following problems. In other words, while the accuracy of monitoring low current charging and the volumetric efficiency of the board are improved, the volumetric efficiency of the power supply connectors 1 themselves drop, enlarging the power supply connectors 1.
Specifically, in the example shown in FIG. 8, the width size is increased because the large current charging current pin insertion parts 14 functioning as the large current charging connector part and the low current charging current pin insertion parts 15 functioning as the low current charging connector part are arranged horizontally in a line. Furthermore, in the example shown in FIG. 9, the height size is increased because the large current charging current pin insertion parts 14 and the low current charging current pin insertion parts 15 are arranged vertically to form two stages.
In addition, because the amount of heat generated by the large current charging current pin insertion parts 14 is greater than that of the low current charging current pin insertion parts 15, good heat radiation characteristics have to be ensured. For this reason, the large current charging current pin insertion parts 14 are arranged with a predetermined distance or more therebetween and therefore cannot be downsized.
As described above, because the power supply connector applicable to both low current charging and large current charging increases in size, downsizing thereof is strongly desired. Especially for the current charging connector parts generating a large amount of heat, the performance thereof decreases if the heat radiation characteristics are low, which impinges the volumetric efficiency in terms of ensuring reliability. Hence, downsizing of the power supply connector has been a big issue.
Note that demand for the power supply connector applicable to both low current charging and large current charging has been increasing, and consequently technical demand has been rigorous yearly. For this reason, now only simply downsizing the power supply connector, but also ensuring safety in the use thereof and further reduction of the cost are required.